Mechanically induced artifacts are common in inkjet printing. Mechanically induced artifacts can result from a variety of sources, including ink dot placement errors, line feed errors, and nozzle malfunctions and mis-directions. In addition, mechanically induced artifacts can be caused by media or paper shape and thickness, the mechanics of the rollers within the inkjet printer, as well as other mechanical issues.
Mechanically induced artifacts can appear in the printed image in a variety of forms including grainy appearance, color-shifts, or banding in the printed image. In addition, it has been identified that certain colors or half-tone dot patterns are particularly susceptible to defects caused by various mechanically induced artifacts. For example, one banding issue is a top of the form transfer error. This error includes a random ink dot shift at the top of an image during printing caused by mechanical feed issues before the page is fed sufficiently into the inkjet printer. As such, pinch rollers do not exhibit adequate control over the page and do not provide a steady state atmosphere for the page. Likewise, another banding issue is a bottom of the form transfer error. This error occurs toward the bottom of an image when the page leaves the pinch rollers of an inkjet printer, thereby losing a control feature of the printer. Bottom of the form transfer errors are more prevalent in full-bleed printing as compared to non-full-bleed printing. Full-bleed printing is known as printing entirely to the edge of the media sheet without leaving an unprinted margin or border. Media shape and thickness issues also play a role in both errors. In both examples, the error occurs due to the page either being transitioned into the pinch rollers of the inkjet printer (top of the form transfer error) or being transitioned out of the pinch roller of the inkjet printer (bottom of the form transfer error).
In general, mechanically induced artifacts are more visible to the human eye in relatively uniform image areas. Also, mechanically induced artifacts are more visible where the ink dot fill is designed to cover each addressable pixel location on the page with a single ink drop, also known as 100 percent fill.
Previously, one known approach to reduce mechanically induced artifacts is to improve the individual mechanical components of an inkjet printer in an attempt to improve the accuracy of the printer. Another known approach is to print the areas of the image associated with mechanical induced artifacts at a slower speed and with additional passes, in an attempt to correct the problems. Yet another approach is to stop printing at a transition area, feed the page out a predetermined amount, and then resume printing.
Improving mechanical components is a robust solution, but can be costly in terms of direct material and increased production costs. Printing with additional passes at a slower speed, while generating fewer mechanically induced artifacts, substantially increases the print time for every print job, including images that are not susceptible to mechanism artifacts, thereby reducing the efficiency of the printer. Feeding the page out without printing necessitates an unwanted visual discontinuity where at least one line of addressable pixels does not contain any ink.